Process for making bioabsorbable self-expanding stent

• US 6,719,934 B2
• Filed: 04/25/2001
• Issued: 04/13/2004
• Est. Priority Date: 08/01/1997
• Status: Expired due to Term

• Current Assignee: Boston Scientific Scimed, Inc. (Boston Scientific Corporation)
• Original Assignee: Boston Scientific Scimed, Inc. (Boston Scientific Corporation)
• Inventors: Stinson, Jonathan S.
• Primary Examiner(s): Tentoni, Leo B.
• Application Number:
  US09/843,425
• Publication Number:
  US 20010021871A1
• Time in Patent Office: 1,084 Days
• Field of Search: 264/40.1, 264/103, 264/235, 87/9
• US Class Current: 264/40.1
• CPC Class Codes: A61F 2/01 Filters implantable into blood vessels
• CPC Class Codes: A61F 2/90 characterised by a net-like or mesh-like structure
• CPC Class Codes: A61F 2210/0004 bioabsorbable
• CPC Class Codes: A61L 31/042 Polysaccharides
• CPC Class Codes: A61L 31/044 Collagen
• CPC Class Codes: A61L 31/06 obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds A61L31/041 takes precedence
• CPC Class Codes: A61L 31/148 Materials at least partially resorbable by the body
• CPC Class Codes: C08L 1/02 Cellulose; Modified cellulose
• CPC Class Codes: C08L 67/04 Polyesters derived from hydroxycarboxylic acids, e.g. lactones C08L67/06 takes precedence
• CPC Class Codes: C08L 77/00 Compositions of polyamides obtained by reactions forming a carboxylic amide link in the main chain of polyhydrazides C08L79/06; of polyamideimides or polyamide acids C08L79/08; Compositions of derivatives of such polymers
• CPC Class Codes: C08L 85/02 containing phosphorus
• CPC Class Codes: D04C 1/06 Braid or lace serving particular purposes

Abstract

A self-expanding stent formed from helically wound and braided filaments of bioabsorbable polymers such as PLA, PLLA, PDLA, and PGA.

Claims

1. A process for making a prosthesis, including:

providing a plurality of elongate filaments comprising a bioabsorbable material selected from the group consisting of;

polydioxanone, polycaprolactone, polygluconate, polylactic acid-polyethylent oxide copolymers, modified cellulose, collagen, poly(hydroxybutyrate), polyanhydride, polyphosphoester, poly(amino acids), poly-L-lactide, poly-D-lactide, polyglycolide, poly(alpha-hydroxy acid) and combinations thereof;

braiding the filaments at a braid angle of from about 120 degrees to about 150 degrees on a first mandrel having a first diameter to form a tubular, radially compressible prosthesis structure;

disposing the prosthesis structure on a second mandrel having a second diameter less than the first diameter; and

while the prosthesis structure is so disposed, annealing the prosthesis structure at a temperature between a glass-transition temperature of the bioabsorbable material and a melting temperature of the bioabsorbable material, to form an annealed prosthesis structure having the annealed diameter D when in a free state, less than an initial diameter of the prosthesis structure before said annealing, the annealed prosthesis structure further being radially compressible to reduced diameters less than the annealed diameter D and radially self-expandable from the reduced diameters.

2. The process of claim 1 wherein:

the bioabsorbable material is selected from the group consisting of poly-L-lactide, poly-D-lactide, polyglycolide, and their combinations.

3. The process of claim 1 wherein:

the first diameter is in the range of 3-30 mm, and the second diameter is in the range of 0.2-10 mm.

4. The process of claim 1 wherein:

said annealing is performed for a time period between about five minutes and about two hours.

5. The process of claim 4 wherein:

said time period is between about 10 minutes and about 20 minutes.

6. The process of claim 1 wherein:

said annealing is performed at an annealing temperature in the range of 60-180 degrees C.

7. The process of claim 6 wherein:

the annealing temperature is in the range of 130-150 degrees C.

8. The process of claim 1 wherein:

said annealing further includes selecting the annealed diameter D based on a predetermined radially outward force to be provided by the annealed prosthesis structure when radially compressed to a predetermined fraction of the annealed diameter D.

9. The process of claim 8 further including:

braiding first and second tubular test structures substantially similar to the unannealed prosthesis structure on the first mandrel;

annealing the first and second tubular test structures on respective first and second test mandrels having different diameters, to form respective first and second annealed test structures having different annealed diameters D₁ and D₂;

loading the first annealed test structure, radially compressed, into a delivery system, deploying the first annealed test structure from the delivery system, then measuring a radially outward force exerted by the deployed first test structure when radially constrained to a predetermined fraction of annealed diameter D₁, thereby to obtain a first radial force value;

loading the second annealed test structure, radially compressed, into the delivery system, deploying the second annealed test structure from the delivery system, then measuring a radially outward force exerted by the deployed second test structure when radially constrained to said predetermined fraction of annealed diameter D₂, thereby to obtain a second radial force value; and

using the first and second annealed diameters D₁ and D₂ and the first and second radial force values to compute and thereby select an annealed diameter D corresponding to the predetermined radially outward force.

10. The process of claim 9 wherein:

said using the first and second annealed diameters and radial force values comprises deriving from said annealed diameters and the radial force values a linear equation relating annealed diameters to the radial force values corresponding to the radial force exerted by tubular test structures having the annealed diameters when radially compressed to said predetermined fraction of the annealed diameters.

11. The process of claims 10 wherein:

said predetermined fraction of the annealed diameters is one-half, and the linear equation relating the annealed diameters D to the corresponding radial force values RE is;

12. For prosthesis structures of the type having elongated bioabsorbable filaments braided on a first mandrel and then annealed on a second mandrel to form annealed tubular structures having annealed diameters when in a free state, radially compressible to reduced diameters less than their annealed diameters, and radially self-expandable from the reduced diameters;

a process for selecting an annealed diameter based on a predetermined radially outward force to be provided by a selected annealed tubular structure when radially compressed to a predetermined fraction of the annealed diameter, said process including;

providing first and second prosthesis structures having a first diameter and being of the type formed by braiding bioabsorbable filaments on a first mandrel;

annealing the first prosthesis structure on a first test mandrel to form a first annealed test structure having an annealed diameter D₁ less than the first diameter;

annealing the second prosthesis structure on a second test mandrel different in diameter from the first test mandrel, to form a second annealed test structure having an annealed diameter D₂ less than the first diameter and different from annealed diameter D₁;

radially compressing the first annealed test structure to a reduced diameter D₃ less than diameters D₁ and D₂, allowing the first test structure to radially self-expand to a predetermined fraction of annealed diameter D₁, then measuring a radially outward force exerted by the first test structure when at the predetermined fraction of annealed diameter D₁ to obtain a first radial force value;

radially compressing the second annealed test structure to said diameter D₃, allowing the second test structure to self-expand to said predetermined fraction of annealed diameter D₂, then measuring a radially outward force exerted by the second test structure when at the predetermined fraction of annealed diameter D₂ to obtain a second radial force value; and

using the first and second annealed diameters D₁ and D₂ and the first and second radial force values to compute and thereby select an annealed diameter D corresponding to a predetermined radially outward force.

13. The process of claim 12 wherein:

said using the first and second annealed diameters and radial force values comprises deriving from said annealed diameters and the radial force values a linear equation relating annealed diameters to the radial force values corresponding to the radial force exerted by tubular test structures having the annealed diameters when radially compressed to said predetermined fraction of the annealed diameters.

14. The process of claim 13 wherein:

the predetermined fraction of the annealed diameters is one-half, and the linear equation relating and annealed diameters D to the corresponding radial force values RF is;

15. A process for making a prosthesis, including:

braiding a plurality of elongate bioabsorable filaments on a first mandrel having a first diameter to form a tubular, radially compressible prosthesis structure;

selecting a second mandrel having a second diameter less than the first diameter for annealing the prosthesis structure at an annealed diameter D based on a predetermined radially outward force to be exerted by the annealed prosthesis structure when radially compressed to a predetermined fraction of the annealed diameter D; and

while the prosthesis structure is so disposed, annealing the prosthesis structure at a temperature between a glass transition temperature of the bioabsorable material and a melting temperature of the bioabsorable material, to form an annealed prosthesis structure having the annealed diameter D when in a free state less than an initial diameter of the prosthesis structure before said annealing, the annealed prosthesis structure further being radially compressible to reduced diameters less than the annealed diameter D and radially self-expandable from the reduced diameters.

16. The process of claim 15 wherein:

the elongate bioabsorbable filaments comprise a material selected from the group consisting of;

polydioxanone, polycaprolactone, polygluconate, polylactic acid-polyethylene oxide copolymers, modified cellulose, collagen, poly(hydroxybutyrate), polyanhydride, polyphosphoester, poly(amino acids), poly-L-lactide, poly-D-lactide, polyglycolide, poly(alpha-hydroxy acid) and combinations thereof.

17. The process of claim 15 wherein:

said annealing is performed at annealing temperatures within the range of 60 degrees C. to 180 degrees C.

18. The process of claim 15 wherein:

said annealing is performed for a time period between about five minutes and about two hours.

19. A process for making a prosthesis, including:

providing a plurality of elongate filaments comprising a bioabsorbable material selected from the group consisting of;

polydioxanone, polycaprolactone, polygluconate, polylactic acid-polyethylene oxide copolymers, modified cellulose, collagen, poly(hydroxybutyrate), polyanhydride, polyphosphoester, poly(amino acids), poly-L-lactide, poly-D-lactide, polyglycolide, poly(alpha-hydroxy acid) and combinations thereof;

braiding the filaments on a first mandrel having a first diameter to form a tubular, radially compressible prosthesis structure;

disposing the prosthesis structure on a second mandrel having a second diameter less than the first diameter;

selecting an annealed diameter D based on a predetermined radially outward force to be provided by the annealed prosthesis structure when radially compressed to a predetermined fraction of the annealed diameter D; and

while the prosthesis structure is so disposed, annealing the prosthesis structure at a temperature between a glass-transition temperature of the bioabsorbable material and a melting temperature of the bioabsorbable material, to form an annealed prosthesis structure having the annealed diameter D when in a free state, less than an initial diameter of the prosthesis structure before said annealing, the annealed prosthesis structure further being radially compressible to reduced diameters less than the annealed diameter D and radially self-expandable from the reduced diameters.

20. The process of claim 19 wherein:

the bioabsorbable material is selected from the group consisting of poly-L-lactide, poly-D-lactide, polyglycolide, and their combinations.

21. The process of claim 19 wherein:

the first diameter is in the range of 3-30 mm, and the second diameter is in the range of 0.2-10 mm.

22. The process of claim 19 wherein:

said braiding comprises winding the filaments to form a braid angle of from about 120 degrees to about 150 degrees.

23. The process of claim 19 wherein:

said annealing is performed for a time period between about five minutes and about two hours.

24. The process of claim 19 wherein:

said annealing is performed at an annealing temperature in the range of 60-180 degrees C.

25. The process of claim 19 further including:

braiding first and second tubular test structures substantially similar to the unannealed prosthesis structure on the first mandrel;

annealing the first and second tubular test structures on respective first and second test mandrels having different diameters, to form respective first and second annealed test structures having different annealed diameters D₁ and D₂;

loading the first annealed test structure, radially compressed, into a delivery system, deploying the first annealed test structure from the delivery system, then measuring a radially outward force exerted by the deployed first test structure when radially constrained to a predetennined fraction of annealed diameter D₁, thereby to obtain a first radial force value;

loading the second annealed test structure, radially compressed, into the delivery system, deploying the second annealed test structure from the delivery system, then measuring a radially outward force exerted by the deployed second test structure when radially constrained to said predetermined fraction of annealed diameter D₂, thereby to obtain a second radial force value; and

using the first and second annealed diameters D₁ and D₂ and the first and second radial force values to compute and thereby select an annealed diameter D corresponding to the predetermined radially outward force.

26. The process of claim 25 wherein:

said using the first and second annealed diameters and radial force values comprises deriving from said annealed diameters and the radial force values a linear equation relating annealed diameters to the radial force values corresponding to the radial force exerted by tubular test structures having the annealed diameters when radially compressed to said predetermined fraction of the annealed diameters.

27. The process of claim 26 wherein:

said predetermined fraction of the annealed diameters is one-half, and the linear equation relating the annealed diameters D to the corresponding radial force values RF is;